1. Field of the Invention
The present invention relates to a catalyst activating system in a multi-cylinder internal combustion engine comprising a plurality of fuel injection valves individually corresponding to a plurality of cylinders. A catalytic converter is provided in an exhaust system common to the cylinders, wherein the concentration of oxygen in an exhaust gas can be controlled in order to activate a catalyst within the catalyst converter, when the engine is at a low temperature.
2. Description of the Prior Art
A catalyst activating system is conventionally known, for example, from Japanese Patent Application Laid-open No. 19627/90.
In the above prior art system, the concentration of oxygen in the exhaust gas is increased by stopping the supplying of the fuel into the particular cylinder in a low-temperature state of the engine, thereby promoting the oxidizing reaction in the catalyst to promote the activation of the catalyst. However, if the concentration of oxygen in the exhaust gas is intended to be controlled only by stopping the supplying of the fuel into the particular cylinder in this manner, the concentration of oxygen can be varied only by the control of the number of cylinders to which the supply of the fuel is stopped, and it is difficult to more precisely control the concentration of oxygen in accordance with the operational condition of the engine.